The present invention relates generally to increasing the efficiency and reducing emissions of internal combustion in engines. More particularly, the present invention relates generally to the application of coatings to internal combustion engines for the purpose of reducing unwanted emissions, and more particularly to the application of nickel coated materials to the combustion surfaces of reciprocating piston internal combustion engines to promote fuel combustion efficiency.
Internal combustion engines using hydrocarbon fuels are widely used due to their ability to create mechanical energy from a fuel that provides power for a sufficient time period without requiring complex or large fuel storage associated with the engine. Internal combustion engines may utilize the Diesel cycle, wherein self-ignition of the hydrocarbon fuel is used to initiate combustion of the hydrocarbon fuel. Hydrocarbon fuel used in Diesel cycle engines typically contains heavier petroleum fractions than the hydrocarbon fuel used in engines having spark ignition systems. The fuel having the heavier hydrocarbon fractions is typically called diesel fuel, even though the fuel can be used in spark ignited and spark assisted ignition engines designed to combust the heavier fractions. Engines using diesel fuel are widely used in commercial vehicles due to inherent efficiencies associated with the diesel fuel and the diesel cycle. Fuels utilizing the heavier hydrocarbon fractions tend to be less expensive than fuels using lighter hydrocarbon fractions, due to lower demand and reduced refining costs. The use of the higher fractionated fuel allows diesel fueled engines to utilize a higher compression ratio, resulting in a higher combustion efficiency.
Although diesel fueled engines are preferred in commercial applications, the use of diesel fueled engines is not without room for improvement. Normal operation of diesel fueled engines results in the production of harmful emissions, including soot and unburned hydrocarbon molecules. Diesel fueled engines tend to have higher exhaust emissions, particularly soot, when heavily loaded, or run in an improper state of tuning. Also, the cost of operating a diesel fueled engine is heavily influenced by the cost of the fuel being used in the engine.
The use of catalytic materials in the exhaust stream of hydrocarbon fueled engines has been implemented to reduce unwanted emissions. The catalytic effect in the exhaust stream accomplishes a reduction of unwanted emissions, but accomplishes the reduction of the unburned hydrocarbons downstream from the combustion chamber, such that energy released through the catalytic reaction is not utilized, and must be rejected as waste heat. Thus, the catalytic reaction provides no efficiency in the conversion of the hydrocarbon fuel into mechanical energy.
Technologies such as low heat rejection (LHR) coatings are being developed to improve the efficiency of fuel combustion in diesel fueled engines. LHR engines rely on the use of combustion surface coatings which form insulation or thermal barriers, thus retaining the heat of combustion within the combustion volume, allowing more of the combustion energy to be converted into mechanical energy, thus reducing the fuel consumption for a given power level. LHR technologies are presently directed towards the use of ceramic coatings applied to the combustion surfaces of an engine to inhibit heat transfer from the combustion products to the engine block and heads. The use of ceramic materials, however, raises issues related to lubrication of the reciprocating components, as well as to the formation of deposits on the coating surfaces (referred to as xe2x80x9ccokingxe2x80x9d) which inhibit combustion efficiency.
U.S. Pat. No. 5,987,882 to Voss et al. is directed towards combining a ceramic layer with an oxidation catalyst material, such as a rare-earth metal oxide. The described multi-component coating is claimed to increase the efficiency of combustion by retaining heat within the volume where the coating is applied. A benefit associated with such retention is an improved performance of the catalyst material, due to increased chemical action of the catalyst at elevated temperatures. Application of the coating to combustion surfaces of a reciprocating engine is described in the patent. The application described requires the integration of a bond coat as a bonding substrate below the insulative coating. The bond coat used for the described examples consisted of a 4 mil metal-aluminum-chromium-yttrium alloy, preferably using nickel, cobalt, or iron for the metallic component.
The use of rare-earth metallic oxide catalytic materials is, may be, however, susceptible to poisoning of the catalyst material. Sulfur contained in fuel to which the catalyst material is exposed prevents catalysts from functioning properly by causing sulfate production that inhibits catalyst regeneration. Accordingly, the use of catalytic technologies which incorporate materials such as platinum and praeseodymium oxide may be problematic when used with current diesel fuel, which contain sulfur levels sufficient to cause poisoning of the catalyst materials.
Other efforts towards improving the combustion efficiency of diesel fueled engines have been directed towards improved fuel formulations, combustion chamber size and shape, and the use of pre-ignition chambers. Each of these technologies may provide some gain with respect to combustion efficiency, however the costs associated with their implementation are not optimal when considered in light of the commercial applications in which the diesel fueled engines are used. The expense of reformulated fuels directly increases the operating costs of engine utilization. Intricate combustion chamber shapes, pre-ignition chambers, and ceramic-metallic coatings add to the production cost and complexity of the engines, as well as complicate maintenance issues and potentially the reliability of the engines themselves.
The use of coatings on engine components, including diesel fueled engine components, has generally been directed towards reduction of friction between components of the engine. The principal areas of interest have been the walls of the cylinder bore and the sealing rings, which extend between the skirt of a piston and the cylinder bore. U.S. Pat. No. 5,866,518 to Dellacorte et al. describes a composite material for use in high temperature applications. The Dellacorte composite consists primarily of chromium dioxide (60-80% by weight) in a metal binder having at least 50% nickel, chromium, or a combination of nickel and chromium. The greatest proportion of binder described is 60%, such that the highest proportion of nickel used in the coating is 30%, at which point no chromium is included. The Dellacorte patent describes the composite as providing a self-lubricating, friction and wear reducing material to be applied to the sealing rings.
U.S. Pat. No. 5,292,382 to Longo describes a sprayable molybdenum/iron coating which may be sprayed on piston rings as a means of reducing friction. The composition of the Longo material is described as 25-40% molybdenum, 4-8% chromium, 12-18% nickel, and 25-50% iron, with carbon, boron, and silicon additionally included in the composition.
The present invention is directed towards a combustion chamber surface coating and method for applying the coating to improve the combustion efficiency of internal combustion engines, particularly, but not necessarily limited to, those utilizing diesel fuel. The coating improves the combustion efficiency through a catalytic reaction with the hydrocarbon based fuel which causes hydrocarbon molecules to disassociate into free radicals at an accelerated rate. The higher concentration of free radicals drives the combustion reaction to a faster and more complete combustion of the hydrocarbon fuel, thus obtaining energy from the fuel more efficiently, as the more complete combustion provides more power per unit of fuel and less unwanted emissions.
The catalytic reaction is accomplished by providing a nickel surface on components which form the combustion chamber of the engine. The nickel reacts with the hydrocarbon molecules in a catalytic reaction which produces the free radicals. Although the nickel is believed to be the component driving the reaction, the use of a pure nickel surface may be limited only by the inactive characteristics of nickel in providing a surface with sufficient structural characteristics to provide a durable and reliable surface. Accordingly, the nickel may be alloyed with other materials to provide sufficient durability and reliability when used in the combustion chamber environment. Presently, an alloy comprising nickel, chromium, and iron has been employed, however other materials may be substituted, interchanged, or included in the composition as indicated by desired other properties.
The amount of free radicals which can be dissociated from hydrocarbon molecules is generally understood to be dependant on the contact of the hydrocarbon molecules and the nickel, and thus the amount of exposed surface area of the nickel appears to be related to the improvements in combustion efficiency gained. In addition to increasing the coating area, the surface of a coated area may be increased by forming the coating with a less smooth surface. Accordingly, the nickel surface may be formed by applying a coating according to the present invention to surfaces which form the combustion chamber by a high velocity oxygen flame process. This deposition method typically results in a coating having sufficient bonding strength to underlying structure to provide sufficient durability, while providing a surface roughness which limits coking of the engine while providing increased contact area between the nickel and hydrocarbon molecules.
In a first form, the present invention may be embodied in an internal combustion engine having at least one reciprocating component, a bore within which the at least one reciprocating component reciprocates, and a closure over one end of the bore. The reciprocating component has a combustion face. The reciprocating component reciprocates relative to the closure between TDC and BDC positions. A combustion volume is defined at least in part by the combustion face of the reciprocating component, and a surface of the closure. At least a portion of the surfaces which define the combustion volume are coated with a metallic coating which includes nickel, such that when the combustion face is at the position at which the combustion face is at a closest point to the closure, it has been noted that it is preferable to have at least 10% of the surfaces which define the combustion volume are coated with the coating, although lesser amounts of coating may also have efficiency.
In an alternate form, the present invention may be embodied in an internal combustion engine having a combustion volume and a reciprocating piston, with the reciprocating piston having a combustion face and the combustion engine further having a combustion volume. The combustion volume may be bounded by combustion surfaces. The combustion surfaces may include the combustion face of the reciprocating piston. A portion of the combustion surfaces equivalent in area to one tenth or more of the combustion face area is coated with a composition that is exposed to combustion gases. In its form, the composition may include between approximately 2% and approximately 80% nickel, between approximately 10% and approximately 30% chromium, and between approximately 10% and 90% iron, although other compositions may be possible.
In a further form, the present invention may be embodied in a process for reducing particulate emissions in a diesel fuel powered internal combustion engine, wherein the internal combustion engine comprises at least one cylinder having a combustion chamber. The process includes the steps of coating at least a portion of the inner surfaces of the combustion chamber with a composition which may include between 2% and 80% nickel and 10% and 40% chromium, (although other compositions may be possible) where the coating forms a surface exposed to combustion gases.